Fosfomycin Safety in Pregnancy
Fosfomycin is safe to use during pregnancy and is specifically recommended by the European Association of Urology for treating both asymptomatic bacteriuria and symptomatic urinary tract infections in pregnant women, with a single 3-gram dose providing effective treatment. 1, 2
Guideline-Based Recommendations
For asymptomatic bacteriuria in pregnancy:
- The European Association of Urology guidelines explicitly recommend screening for and treating asymptomatic bacteriuria in pregnant women with either standard short-course treatment or single-dose fosfomycin trometamol 1, 2
- This is critical because untreated bacteriuria increases pyelonephritis risk 20-30 fold (from 1-4% with treatment to 20-35% without treatment) 3
For symptomatic UTI in pregnancy:
- Fosfomycin trometamol 3g single dose is recommended as an acceptable first-line alternative to nitrofurantoin for treating symptomatic UTI in pregnant women 3
- The European Urology guidelines list fosfomycin alongside nitrofurantoin and cephalosporins as appropriate first-line therapy 3
Trimester-Specific Considerations
First trimester:
- Fosfomycin is explicitly recommended as an acceptable alternative to nitrofurantoin 3
- This is particularly important since trimethoprim-sulfamethoxazole should be avoided in the first trimester due to teratogenic concerns 3
Third trimester:
- Fosfomycin (single 3g dose) can be considered for uncomplicated lower UTIs, though clinical data for third trimester use is more limited than for cephalosporins 3
- Nitrofurantoin should be avoided near term due to risk of neonatal hemolysis 3
Safety Evidence
Clinical safety data:
- A large multicenter study (PHYTOVIGGEST) analyzing 5,362 pregnancies found no significant differences in gestational age, neonatal weight, Apgar scores, or pregnancy complications (urgent cesarean delivery, need for labor induction) between women taking fosfomycin and those not taking it 4
- Multiple studies confirm fosfomycin is well tolerated with only minor adverse effects during pregnancy 5, 6, 7
Comparative efficacy:
- A meta-analysis found no significant differences in clinical cure rates (RR 0.95% CI 0.81-1.12) or microbiological cure rates (RR 0.96,95% CI 0.84-1.08) between fosfomycin and nitrofurantoin for uncomplicated UTI and asymptomatic bacteriuria in pregnancy 8
- A clinical study in pregnant women showed 95.2% therapeutic success with single-dose fosfomycin versus 90.0% with 3-day ceftibuten (not statistically significant) 6
Dosing and Administration
Standard regimen:
- Single 3-gram oral dose of fosfomycin tromethamine 1, 2, 3
- Provides therapeutic urinary concentrations for 24-48 hours, sufficient to eradicate most uropathogens 2, 7
Treatment duration:
- For asymptomatic bacteriuria: single-dose or standard short-course (7-14 days if using other agents) 1, 3
- For symptomatic cystitis: single 3-gram dose is equivalent to 7-10 day courses of other antibiotics 5, 6
Critical Clinical Caveats
When NOT to use fosfomycin:
- Do not use for pyelonephritis or upper UTIs—insufficient efficacy data for these conditions 2
- For suspected pyelonephritis, use cephalosporins that achieve therapeutic blood concentrations 3
Renal impairment considerations:
- Use with caution in patients with renal insufficiency, as elimination half-life increases from 5.7 hours to 40-50 hours in anuric patients 2
- However, this primarily applies to IV formulations; oral fosfomycin for uncomplicated UTI remains appropriate
Essential follow-up:
- Always obtain urine culture before initiating treatment to guide therapy 3
- Follow-up urine culture 1-2 weeks after completing treatment is recommended to confirm cure 3
- If symptoms do not resolve or recur within 2 weeks, obtain repeat culture and consider alternative agents 1